MID TEST (UTS) Basic Chemistry I

1. 
   
   
   
   
   
     Question :
   1.   pure substance X is solid at room temperature. if the substance is heated to 230⁰C is melted gradually. if then cooled to room temperature, the liquid can not be frozen
   a.        is it possible X of an element or a compound. explain it!
   
   
   answer :
   I think X is a compound substance because the substance X there is a temperature or temperature where it shows the boiling point and melting point where the reaction can be smelted though gradually. And also substance X indicates the compound is ionic compound shown by the boiling point and high melting.
   
   
   b.      does it a chemical change occured? if so can it be said to undergo an endoterm changing, based on the information provided?
   
   
   answer :
   Substance X can be regarded as a change when heated at a temperature of 2300C occurred a little fusion, albeit slightly. Consolidation is changing the substance X from solid to liquid.
   
   
   c.       Can it be said that the liquid is an element, based on the information provided
   
   
   answer :
   I think that could be because the elements are part of the underlying basis of something where, the fluid element is an element that is composed of elements / structure of an element that is liquid or liquid. such as hydrogen and oxides that react to H2O.  
   
     Question :
   2.       When a candle that weight 10 gr is burned in oxygen, carbon dioxide and water vapor formed by combustion the weight more than 10 gr. Was this case match with the law of mass. Explain it.
   
   
   answer :
   It is not contrary to the law of conservation of mass, due to the law of conservation of mass is explained that the mass of a substance before and after the same or unchanged. And also in the reaction above Hannya weight change and explained that there was no mass change. So it belongs to the law of conservation of mass.
   
     Question :
   3.       When carbon burns in oxygen under limited number, it will form two gaseous compounds. Suggest the way to differentiate the two compounds with one another.
   
   
   answer :
   In my opinion, to differentiate the two compounds formed from carbon gas that burns oxygen. To do the experiment qualitatively to distinguish or know the chemical to know the difference.
   
     Question :
   4.       After mendeev compiled theperiodic table, he conclude that the atomic weight of certain elements was wrong ruling, and this conclusion was apparently correct. How Mendeleev was able to predict that several atomic weight were wrong? Why his predictions are not always right. Explain!
   
   
   answer :
   Predictions are not always correct because the periodic Mendelev, long periods in the periodic system are not the same and why not described. That is what makes his predictions are not always right.
   
     Question :
   5.       When an aqueous mercury chloride solution is added to an aqueous solution of silver nitrate, a white solid forms. Identify the white solid and write the balanced equation for the reaction that occurs.
   
   
   answer :
   HgCl₂ + 2AgNO₃ à Hg (NO₃)₂ + 2AgCl